The first 'dev' argument is normally the struct device pointer of a pci_dev,
usb_device or platform_device. It is rare for dev to be NULL, but it happens
-with ISA devices, for example.
+with ISA devices or when one device creates multiple PCI devices, thus making
+it impossible to associate v4l2_dev with a particular parent.
+
+You can also supply a notify() callback that can be called by sub-devices to
+notify you of events. Whether you need to set this depends on the sub-device.
+Any notifications a sub-device supports must be defined in a header in
+include/media/<subdevice>.h.
You unregister with:
Unregistering will also automatically unregister all subdevs from the device.
+If you have a hotpluggable device (e.g. a USB device), then when a disconnect
+happens the parent device becomes invalid. Since v4l2_device has a pointer to
+that parent device it has to be cleared as well to mark that the parent is
+gone. To do this call:
+
+ v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
+
+This does *not* unregister the subdevs, so you still need to call the
+v4l2_device_unregister() function for that. If your driver is not hotpluggable,
+then there is no need to call v4l2_device_disconnect().
+
Sometimes you need to iterate over all devices registered by a specific
driver. This is usually the case if multiple device drivers use the same
hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv
v4l2_device_call_all(). That ensures that it will only go to the subdev
that needs it.
+If the sub-device needs to notify its v4l2_device parent of an event, then
+it can call v4l2_subdev_notify(sd, notification, arg). This macro checks
+whether there is a notify() callback defined and returns -ENODEV if not.
+Otherwise the result of the notify() call is returned.
+
The advantage of using v4l2_subdev is that it is a generic struct and does
not contain any knowledge about the underlying hardware. So a driver might
contain several subdevs that use an I2C bus, but also a subdev that is
calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
If all goes well, then it registers the subdev with the v4l2_device. It gets
the v4l2_device by calling i2c_get_adapdata(adapter), so you should make sure
-that adapdata is set to v4l2_device when you setup the i2c_adapter in your
-driver.
+to call i2c_set_adapdata(adapter, v4l2_device) when you setup the i2c_adapter
+in your driver.
You can also use v4l2_i2c_new_probed_subdev() which is very similar to
v4l2_i2c_new_subdev(), except that it has an array of possible I2C addresses
Both functions return NULL if something went wrong.
+Note that the chipid you pass to v4l2_i2c_new_(probed_)subdev() is usually
+the same as the module name. It allows you to specify a chip variant, e.g.
+"saa7114" or "saa7115". In general though the i2c driver autodetects this.
+The use of chipid is something that needs to be looked at more closely at a
+later date. It differs between i2c drivers and as such can be confusing.
+To see which chip variants are supported you can look in the i2c driver code
+for the i2c_device_id table. This lists all the possibilities.
+
struct video_device
-------------------
- ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance
(highly recommended to use this and it might become compulsory in the
future!), then set this to your v4l2_ioctl_ops struct.
+- parent: you only set this if v4l2_device was registered with NULL as
+ the parent device struct. This only happens in cases where one hardware
+ device has multiple PCI devices that all share the same v4l2_device core.
+
+ The cx88 driver is an example of this: one core v4l2_device struct, but
+ it is used by both an raw video PCI device (cx8800) and a MPEG PCI device
+ (cx8802). Since the v4l2_device cannot be associated with a particular
+ PCI device it is setup without a parent device. But when the struct
+ video_device is setup you do know which parent PCI device to use.
If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or
.ioctl to video_ioctl2 in your v4l2_file_operations struct.
projects / firefly-linux-kernel-4.4.55.git / blobdiff